Web drying tunnel

ABSTRACT

An elongate moving web passing through a drying tunnel is supported along a slightly arched path by pressurized air directed against its concave lower face. The arched path of the web tends to prevent it from bowing transversely, thereby facilitating maintaining it in central relation to the tunnel by means of the air escaping upwardly around its edges. Additionally, the resulting profile of the web inherently reduces its tendency to wrinkle or sag, thus allowing it to be drawn through the tunnel under relatively low longitudinal tension.

United States Patent Inventors John A. McClenathan;

Donald L. Nielsen, Beloit, Wis. 4,293

Jan. 20, 1970 May 4, 1971 Beloit Corporation Beloit, Wis.

Appl. No. Filed Patented Assignee WEB DRYING TUNNEL 7 Claims, 4 DrawingFigs.

US. Cl. 34/156 Int. Cl F261 13/00 FieldofSearch 34/156, 10

References Cited UNITED STATES PATENTS 12/1907 Cohen 3,287,821 11/1966Schregenberger 3,324,570 6/1967 Flaithetal Primary Examiner-Carroll B.Dority, Jr. Attorneys-Dirk J Veneman, John S. Munday and Gerald A.

Mathews ABSTRACT: An elongate moving web passing through a drying tunnelis supported along a slightly arched path by pressurized air directedagainst its concave lower face. The arched path of the web tends toprevent it from bowing transversely, thereby facilitating maintaining itin central relation to the tunnel by means of the air escaping upwardlyaround its edges. Additionally, the resulting profile of the webinherently reduces its tendency to wrinkle or sag, thus allowing it tobe drawn through the tunnel under relatively low longitudinal tension.

PATENTED m 4mm SHEET 1 [IF 2 JOHN A. McCLENATHAN DONALD L. NIELSENPATENTEDMAY 415m 3577.653

' same or 2 v JOHN A. MCCLENATHAN DONALD L. NIELSEN INVENTORS iii am WEBDRYING TUNNEL BACKGROUND OF THE INVENTION I 1. Field of the Invention 1The present invention relates to web-dryers and more particularly todryers in which a moving elongate web is supported by air cushion meansas it passes through a dryer tunnel.

2. Description of the prior Art It is well known in the prior art tosupport an elongate moving web by air cushion means as it is drawnthrough a drying chamber, thereby avoiding physical contact between theweb and the dryer structure to eliminate the attendant possibility ofscratching or otherwisedamaging the web. In such prior art dryers,however, a web has either been supported in a flat plane as it movesthrough an elongate tunnel or has been draped in vertical loopssupported by semicylindrical air cushion devices as it passes through ananalogous-drying chamber.

If the web being dried is very thin and flexible, for example a web ofrecording tape comprising a plastic film base coated with a layer ofmagnetic material, the former type of dryer tunnel is not entirelysatisfactory for drying the magnetic coating because of the coatingdifficulty in maintaining the very flexible web in'central relation tothe tunnel without bringing it into physical contact with structuralguide means or subjecting it to excessive longitudinal tension. In otherwords, if the tape tends to drift sideways in the tunnel, the 'flow ofair around its edges in'such prior art dryers will simply flex or ripplethe web transversely rather than restoring it to its initial centralpath unless the web is under relativelygreat longitudinal tension.Furthermore, such-transverse flexing or rippling of the web is very aptto promote permanent wrinkling, creasing or localized stretching, whichis totally unacceptable in the finished product.

In the other above-mentionedtype of dryer device,the difficultyencountered in centering the web is reduced because of the fact that itis bowed quite abruptly around the air cushion support members above andbelow its draped vertical portions and therefore resists transversedeformation in its supported arcuate areas. However, this approach islikewise undesirable for drying magnetic tape or the like, whichrequires that the web be maintained in a relatively horizontal plane toprevent the web coating from running or sagging during the initial stageof the drying process.

SUMMARY OF THE INVENTION The present invention involves the discoverythat only a relatively slight arched curvature need be imposed on a webof very thin flexible material supported. by air cushion means in ahorizontal tunnel type dryer in order to achieve a very signifi cantimprovement in the smoothness and self centering action of the web whileat the same time reducing the longitudinal tension to which it must .besubjected during the drying process. Accordingly, a dryer tunnelaccording to the invention is provided with a permeable support memberwhich is slightly arched toward the center of the tunnel and throughwhich pressurized air is blown against the lower face of the web tosupport the web along a correspondinglyarched path. By reason of itslongitudinal curvature, transverse movement of the web is discouragedand stabilized to the extent that the air passing upwardly around theedges of the web suffices to keep it centered in the tunnel withoutresort to elaborate air control or pressure regulating'means. Due to therelatively slight longitudinal and transverse curvature encountered bythe web. the invention also substantially eliminates the problem ofgravitational sagging or flow of the liquid coating on the top surfacethereof. Furthermore, by virtue of the absence of internal movingmechanical elements and because of the simplified air curtain meansemployed for preventing leakage of solvent vapors and drying air out ofthe ends of the,

dryer unit, the extremely versatile and economical construction of sucha dryer tunnel is particularly suitable for apble solvents or the like.

Various means for practicing the invention and other advantages andnovel features thereof will be apparent from the following detaileddescription of an illustrative preferred embodiment of the invention,reference being made to the accompanying drawings in which likereference numerals denote like elements. I

In the accompanying drawings:

FIG. I is a schematic front elevational illustration of a typical webdrying tunnel installation according to a preferred embodiment of. thepresent invention;

v FIG. 2 is a fragmentary front elevational view of one of the sectionsof the dryer tunnel depicted schematically in FIG. 1;

.FIG. 3 is a cross-sectional end view taken along 3-3 of FIG.

2; and v FIG. 4 is a fragmentary cross-sectional plan view taken alongline 440i" FIG. 2.

' DESCRIPTION 01% THE ILLUVSTRATIVIE'PREFIERRED I .EMBODIMENT Referringfirst to FIG. I of the drawings, the illustrative dryer tunnel will beseen to comprise six generally similar boxlike sections I] through l6joined together between similar endsections 17 and 18.to provide anelongate arched tunnel structure through which web l9 moves from left toright as indicated by arrows 21. As shown in FIGS. 2, 3 and 4, each ofthe dryer sections is of generally rectangularcross section and isprovided with slightly sloped end flanges 22 by which the sections arebolted to each other and to end sections I7 and I8, whereby theassembled unit is in effect a single selfsupporting unitary structure. v

An aperture plate 23, provided with narrow elongate transverse slots 24.is supported within each of the tunnel sections by angle members 25along the sidewalls thereof. Each aperture plate is bent downwardly atone end to provide a lip 26, which is overlapped by the opposite end ofthe similar plate in the next tunnel section. A curtain plate 27 issandwiched between the connected flanges of sections 13 and 14 at thecenterof the tunnel and is provided with a horizontal slot 28 whichaccommodates the moving web. Similar curtain members are also providedat the ends of sections 17 and 18, as indicated by numeral 29.Accordingly, it will be seen that the portion of the tunnel betweencurtain plates 29 comprisessix separate lower chambers-30 in thecorresponding tunnel sections, whereas the upper portion of the tunnelis divided into only two chambers or zones 31 and 32 definedbetween thecentral curtain plate 27 and the similar plates 29 at the ends of tunnelsections I1 and I6. 7

Each of the two zones of the dryer tunnel is connected with acorresponding air supply and exhaust system comprising a main heatingand filtering blower 33 which delivers heated air into one end of itscorresponding zone through an inlet duct 34 so that the drying airpasses along the upper face of the moving web before being exhausted atoutlet duct 36 connected to exhaust blower 37. Part of the exhaust airis reir ttroduced into the main heating and filtering blower forhumidity control purposes, as is well known in the dryer art. A

supplemental blower 38 derives heated air fromthe correspondingmain'blower unit and feeds it into the lower tunnel chambers 29 througha manifold 39 and inlet ducts 40 at a 4-, the web is somewhat wider thanslots 24 in the aperture I plates but narrower than the tunnel itself sothat the pressurized air impinging on the lower web surface escapesupwardly around the edges of the web into the drying zones and therebytends to center the web in the tunnel.

in a typical. embodiment of the invention adapted to handle a webapproximately 2 feet wide, the overall tunnel was longer and comprisedmore tunnel sections than the illustrative-embodiment shown in FIG. 1,having a total length of about 80 feet and effective radius ofapproximately 200 feet. in other words, the moving web within the tunnelwas elevated approximately 4%feet at its center along a substantiallyarcuate arch path subtending an angle of approximately ll'r from eachideof a vertical line rassing through the center of the tunnel.

Although the illustrated individual aperture plates are flat, it will beobvious that they could be slightly curved to define a perfectly arcuatesurface, but the essential requirement is not that the support surfacebe a perfect are but rather that either the true or approximate arc ofthe moving web be of sufficient curvature to stabilize it withoutsloping it out of a relatively horizontal path. As illustrated in FIG.3, the edges of the web will droop slightly notwithstanding thelongitudinal web curvature, but this effect actually tends to improverather than detract from the tendency of the web to center itself in thetunnel. Although the longitudinal curvature of the web can varyconsiderably, depending on the flexibility and thickness of theparticular web material being processed, it would generally not exceedan arc subtending an angle of more than 20 at either side of thevertical centerline nor would the effective radius of curvature of thesupport surfacedefined by the aperture plates generally be less than 25times the width dimension of the web support surface.

The end sections 17 and 18 of the dryer, which are of the same type ofconstruction as tunnel sections 11 through 1.6, are provided withrespective entrance and exit curtain plates 41 and 42 similar to thecorresponding plates 27 and 29. In these end sections, the previouslydescribed aperture plates are omitted so that the web itself serves todivide each end section into upper and lower chambers 43 and 44 incommunication with each other along the edges of the web. Each of theend sections is associated with an input blower 45 which forces unheatedair into the upper and lower chambers of that section through respectiveupper and lower inlet ducts 46 and 47 and with exhaust blower 37 whichremoves air from the same upper and lower chambers through respectiveupper and lower exhaust ducts 48 and 49. Accordingly, a relatively highvolume of unheated air flows within the end sections along flow pathsindicated generally by arrows 51, thereby providing air curtain sealingmeans to prevent solvent vapors or the like from escaping into thesurrounding environment from the ends of the dryer.

The invention has been described in detail with particular reference toan illustrative preferred embodiment thereof but it will be apparentthat variations and modifications can be effected within the spirit andscope of the invention as described hereinbefore and as defined in theappended claims.

We claim:

1. An apparatus for drying a longitudinally moving flexible web, saidapparatus comprising:

a. means defining an elongate tunnel through which said web travelslongitudinally,

b. permeable support plate. means defining an air penneable supportsurface within said tunnel, said support surface being generally flat intransverse relation to said tunnel and arched longitudinally of saidtunnel approximately along an imaginary arc subtending an angle of lessthan 20 at either side of an imaginary vertical radius of that arc,

c. first air supply means for supplying pressurized heated dryi g air toand exhausting such air from said tunnel above said support plate means,and Y second air supply means for supplying web supporting air to saidtunnel below said support plate means at a pressure greater than that ofsaid heated drying air, whereby said web supporting air blows upwardlythrough said support plate means and impinges on the lower face of theportion of said web moving through said tunnel to thereby support thatportion of said web out of contact with the physical structure of saidtunnel along an arched web path generally parallel to said support platesurface.

2. An apparatus according to claim 1 including air curtain means atopposite ends of said tunnel providing barriers to the flow of saidheated drying air out of said tunnel through said opposite ends thereof.'I

3. An apparatus according to claim 1 including internal baffle meansdividing the portion of said tunnel above said support plate means intoa plurality of drying zones, said second air supply means being adaptedto deliver heated drying air to and exhaust such air from each of saidzones independently of one another.

4. An apparatus according to claim 1 in which said imaginary radiusapproximately defining the longitudinal curvature of said supportsurface is at least 25 times larger than the width of said supportsurface within said tunnel. v

5. An apparatus according to claim 1 in which said support plate meansis provided with a plurality of narrow parallel air conductive slotsdisposed transversely of said tunnel.

6. An apparatus according to claim 1 in which said tunnel comprises aplurality of straight tunnel sections provided with respectivesubstantially flat support plate means, said tunnel sections includingslightly angled end flanges which are adapted to be joined together toestablish a polygonally arched tunnel profile and a correspondingpolygonally arched support surface approximating the curvature of saidimaginary arc.

7. The invention defined by claim 6 in which said tunnel sections joinedtogether by said end flanges thereof provide a rigid self-supportingtunnel structure.

1. An apparatus for drying a longitudinally moving flexible web, saidapparatus comprising: a. means defining an elongate tunnel through whichsaid web travels longitudinally, b. permeable support plate meansdefining an air permeable support surface within said tunnel, saidsupport surface being generally flat in transverse relation to saidtunnel and arched longitudinally of said tunnel approximately along animaginary arc subtending an angle of less than 20* at either side of animaginary vertical radius of that arc, c. first air supply means forsupplying pressurized heated drying air to and exhausting such air fromsaid tunnel above said support plate means, and d. second air supplymeans for supplying web supporting air to said tunnel below said supportplate means at a pressure greater than that of said heated drying air,whereby said web supporting air blows upwardly through said supportplate means and impinges on the lower face of the portion of said webmoving through said tunnel to thereby support that portion of said webout of contact with the physical structure of said tunnel along anarched web path generally parallel to said support plate surface.
 2. Anapparatus according to claim 1 including air curtain means at oppositeends of said tunnel providing barriers to the flow of said heated dryingair out of said tunnel through said opposite ends thereof.
 3. Anapparatus according to claim 1 including internal baffle means dividingthe portion of said tunnel above said support plate means into aplurality of drying zones, said second air supply means being adapted todeliver heated drying air to and exhaust such air from each of saidzones independently of one another.
 4. An apparatus according to claim 1in which said imaginary radius approximately defining the longitudinalcurvature of said support surface is at least 25 times larger than thewidth of said support surface within said tunnel.
 5. An apparatusaccording to claim 1 in which said support plate means is provided witha plurality of narrow parallel air conductive slots disposedtransversely of said tunnel.
 6. An apparatus according to claim 1 inwhich said tunnel comprises a plurality of straight tunnel sectionsprovided with respective substantially flat support plate means, saidtunnel sections including slightly angled end flanges which are adaptedto be joined together to establish a polygonally arched tunnel profileand a corresponding polygonally arched support surface approximating thecurvature of said imaginary arc.
 7. The invention defined by claim 6 inwhich said tunnel sections joined together by said end flanges thereofprovide a rigid self-supporting tunnel structure.